DC electronic power supplies, such as flyback circuits, can use an unregulated DC voltage supply and a DC to DC converter that converts the unregulated voltage into a regulated output DC voltage that can be used for applications requiring such a regulated DC supply, such as certain electronic circuitry, inverters or electric motors. A common feature of such DC to DC converters is the requirement for galvanic isolation between the unregulated DC voltage bus and the regulated output voltage.
While knowledge of the voltage at the unregulated DC supply can be beneficial, direct detection of the unregulated supply can be problematic as such detection circuitry can involve additional components for isolating the unregulated source from the regulated power supply. Indirect detection can suffer from inaccurate measurements that are not reflective of the present value of the voltage on the unregulated side. For example, relatively short transients or sudden withdrawal of the unregulated DC supply may not be reflected in a sample and hold peak detection circuitry. Such circuitry can be in the form of an RC circuit for which the chosen time constants can be too long to react to phenomenon occurring at time scales shorter than the RC time constant.